Fluidised beds



-De. 9, 1969 J. G. LARKHAM 3,482,328-

FLUIDISED BEDS Filed May 24, 1968 2 Sheets-Sheet 1 J. G. LARKHAMFLUIDISED-BEDS Filed May 24, 1968 2 Sheets-Sheet 2 United States Patent3,482,328 FLUIDISED BEDS John George Larkham, Nailsea, Bristol, England,assignor to The Imperial Tobacco Company (of Great Britain and Ireland),Limited, a company of England Filed May 24, 1968, Ser. No. 731,765Claims priority, application Great Britain, June 15, 1967, 27,570/ 67Int. Cl. F26b 17/14; B65g 53/34 US. Cl. 3457 6 Claims ABSTRACT OF THEDISCLOSURE A tower horizontally vibrated and comprising fluidisingchambers arranged one below the other with vertical overflow ducts fortransferring the fluidised material from one chamber to the nextchamber, wherein the outlet from each duct is provided with apressure-responsive flap valve.

This invention relates to fluidised beds wherein materials in granularor other flowable form are fluidised by subjecting them to an upwardlyflowing stream of gas. Such fluidised beds may be used for example fordrying or for moistening the material, for the recovery of solvents,therefrom, and so on.

In particular, the invention may be used to extract nicotine from dampground tobacco by passing steam therethrough. Such material presents aspecial problem because it is.cohesive and it has therefore been foundnecessary to vibrate the fluidised bed transversely to the upward flowof steam. If vibration is not carried out, the steam blows holes throughthe tobacco, forming discrete passages and not disturbing the remainderof the tobacco bed.

Apparatus for the treatment of solids in granular form has already beenproposed wherein the solids are fed on to the uppermost of a. pluralityof horizontal screens in a screen unit which is vibrated both with avertical movement and with an orbital horizontal movement. Gas is passedupwards through the vibrating screens and withdrawn from the top of theapparatus. The solids are conveyed downwards from screen to screen byducts, each of which has its inlet at the side of the apparatus and itsoutlet adjacent the centre of a screen. Each duct has a short verticalintake section followed by a long inwardlyextending section which isinclined slightly below the horizontal. The ducts may be of valve typeconstruction to minimise the passage of the gas through them.

Such a prior proposal would not be suitable for dealing with a cohesivematerial such as damp ground tobacco because the vertical vibrationwould tend to compact the tobacco making it resistant to penetration bythe gas whilst the inclined ducts, if provided with valves to excludethe gaseous upflow, would rapidly become choked by the tobacco. Also,mere screens would not provide the pressure drop in the gas which isrequired .by our invention when applied to thick fluidised beds ofcohesive material.

According to the present invention, there is provided apparatus forurging material into a fluidised state and comprising a tower divided byperforated flooring into a plurality of fluidising chambers arranged onebelow the other, overflow ducting for transferring material undergravity from one chamber to the chamber below it, an inlet for feedingmaterial to the top chamber and an outlet for withdrawal of the materialfrom the bottom chamber, an inlet for gas in the bottom chamber and anoutlet for gas in the top chamber, and means for vibrating the materialhorizontally in the chambers, wherein the overflow ducting is at leastsubstantially vertical, the flooring is perforated to produce a pressuredrop in the gas as it flows upwards through it, and the outlet of eachoverflow ducting is controlled by a flap valve responsive to thedifferential pressure of opposing operational pressures in theapparatus.

Preferably, each flap valve when closed is arranged to be urged open bythe weight of material and the pressure of the gas in the overflowducting against the pressuredof the gas in the chamber in which thevalve is 10- cate Preferably, each flap valve is rectangular andcontrols a rectangular outlet in an overflow ducting, the valve beinghinged along its top to the ducting and sealed along its sides to theducting by means of flexible web members.

The invention is illustrated by way of example in the accompanyingdrawings in which:

FIGURE 1 is a diagrammatic vertical section through apparatus embodyingthe present invention,

FIGURE 2 is an enlarged perspective view of ducting with a flap valveaccording to the present invention, and

FIGURES 3, 4 and 5 illustrate the operation of the flap valve of FIGURE2.

Referring to the drawings and particularly FIGURE 1, a vertical towercomprises three fluidising chambers 11, .12 and 13 disposed one abovethe other. There may of course be more than three chambers. The chambershave flooring 11a, 12a, 13a respectively which are perforated to producean appreciable pressure drop in an upflow of steam through the tower 10from a steam inlet 14 at the bottom to a steam outlet 15 at the top ofthe tower, the flow of steam being indicated by feathered arrows. -Atthe top of the tower is a material inlet 16 through which dam-p groundtobacco, which has been treated with a suitable alkali, is passed intothe top chamber 1.1.

A vertical overflow duct 17 transfers the overspill of ground tobaccofrom chamber 11 down to chamber 12 below it, whilst a further verticaloverflow duct 18 transfers the overspill of ground tobacco from chamber12 to chamber 13. Finally, a third vertical overflow duct 19 transfersthe overspill of tobacco from chamber 13 to a material outlet 20provided in the base of the tower, the zig-zag passage of ground tobaccothrough the tower 10 being indicated by plain arrows. Each of the ducts17 and 18 is provided at its lower end with a pressure-sensitive flapvalve which is urged towards its open position by the weight of groundtobacco in the duct falling upon it and the pressure of the steam in theduct but is urged towards its closed position by the pressure of thesteam in the chamber in which the valve is located. In this way thetobacco is passed downwards from chamber to chamber but any appreciableflow of steam is prevented from passing upwards through any of thetransfer ducting.

To avoid condensation in the tower 10, the latter may be fitted with asteam jacket (not shown).

In operation, the tower 10 is filled with damp tobacco to the conditionshown in FIGURE 1 so that tobacco fills each of the chambers 11, 12, 13up to the level of the inlet of its overflow duct, say three to fourinches above the flooring, while steam is blown upwards through thetower to pass through the bed of tobacco in each of the chambers 11 to13. Arms 21, 22, 23, 24 which are pivotally attached to the outersurface of the tower are driven via eccentrics to vibrate the tower 10in a substantially horizontal plan in order to avoid the formation ofblowholes in the tobacco beds.

The resulting vibration of the tobacco within the chambers 11, 12 and 13and the up flow of steam through-the tobacco result in fluidisation ofthe tobacco, further tobacco being fed into the tower 10 through inlet16- to provide a continuous flow of tobacco through the tower. The steamleaving outlet 15 contains nicotine which can then be recovered orconcentrated in subsequent known apparatus.

Details of the automatic pressure sensitive flap valves 30 are shown inFIGURES 2 to 5. Referring to FIGURE 2, the overflow duct 17 is shownprovided at its lower end with an inclined bottom wall 31, which slopesdownwards to a rectangular outlet 32. The inclination of the bottom wall31 assists the discharge of the tobacco. through the outlet. Hinged tothe upper edge of outlet 32 is a rigid flap 33 which is sealed along itsopposing sides by means of flexible webs 34, 35 which connect the flapto the side edges 36, 37 of the outlet 32. The flaps 33 and the webs 34,35 may be of nylon proofed with nitrile rubber, the flap being threetimes thicker than the webs in order to obtain the necessary stiffness.The webs have the flexibility of a suitable bellows-like material. In anopen position of the flap 33, as shown in FIGURE 2, an outlet port 40'is defined by the lower side 41 of outlet 32, the lower edges of webs34, 35 and the lower edge of flap 33. In the closed position of flapvalve 30, the flap 33 covers the outlet 32 of duct 17 preventing anyappreciable flow of material or gas therethrough. Due to the simpleattachment of the flap valve 30 to duct 17, its operation is controlledon the one hand by the weight of material and the pressure gas withinthe duct 17 and on the other hand by the pressure of the gas upon itsouter surface. Thus the pressures which control the valve 30 are thoseexerted by the weight of tobacco within duct 17 and the difference inpressure of the steam between chambers 12 and 11.

Referring now to FIGURE 3 the flap 33 is shown in its closed position inwhich the webs 34, 35 collapse like a bellows, permitting the flap 33 toseal against the outlet 32 of the duct 17. In this position, thesuperior steam pressure in chamber 12 maintains the flap 33 closed andthus the steam is prevented from passing upwardly through the duct 17 sothat tobacco is permitted to accumulate within the duct 17.

As shown in FIGURE 4 sufiicient tobacco has accumulated within duct 17to form a wedge and overcome the pressure on the flap 33 exerted by thesteam within chamber 12 and thus the flap 33 is shown partially open toallow tobacco to pass therethrough into the chamber 12. As soon as theweight of the tobacco within duct 17 is insufficient to overcome thepressure on flap 33 by the steam within the chamber 12 the flap willautomatically reclose.

Referring now to FIGURE the flap 33 is shown fully open, permitting theoptimum flow of tobacco through duct 17 and into chamber 12. In thisposition the lower edges of the webs 34, 35 enter the tobacco withinchamber 12. Thus the tobacco within chamber 12 effectively forms a sealaround the outlet port 40 and prevents any appreciable flow of steamtherethrough into the duct 17. It will be noted that the lower edge ofthe duct outlet 32 is substantially level with the inlet 50 to the duct18 which is of course the transfer duct from chamber 12 to chamber 13.This feature helps to keep the flap 33 open-and so promote a constantflow of tobacco through the duct 17. It will be appreciated that duringnormal operating conditions of the apparatus, the positions ofeach valve30 should remain substantially as shown in FIGURE 5, with each flap 33open to its maximum extent to permit a maximum through-flow of tobacco.

, Should one of the transfer ducts, e.g. duct 17, become starved oftobacco the level in the chamber 12 will tend to fall, the weight of thetobacco within duct 17 will decrease and the flap valve will commence toclose under the pressure of the steam within chamber 12. The positionillustrated in FIGURE 4 may then be reached. Complete closure of thevalve 30 may ensue, but if not, little steam will pass upwards throughthe nearly closed valve and the apparatus can automatically reprime andrestart itself once the supply of tobacco is available at the inlet .4to the apparatus. One advantage of the webbed flap valve 1s that it doesnot become clogged by the damp cohesive tobacco. Thus there is no needto prime the apparatus by hand, nor to control operation of the valveaccording to the level of material in each of the chambers, and alsothere is no need to control flow of material in accordance with the flowof steam, as this will all be done automatically. The apparatus is notof course limited to the treatment of tobacco by steam.

In a modification of the apparatus, each valve 30 is operatedautomatically by control apparatus which is sensitive to pressuresexisting in the tower. Thus for example a flap valve could be actuatedby mechanism sensitive to pressures within the duct 17 and the chamber12 without permitting the pressures themselves to control directly theoperation of the valve. Again, operation of the valve could becontrolled according to pressures existing elsewhere in the tower asrequired.

The particular form of the valve illustrated need not be employed andany suitable shape of exit can be used. Two outlets may be formed inopposing sides of the duct 17 instead of a single outlet from the front,in which case the bottom wall 31 would be V-shaped with its apexpointing upwards so as to divide the flow of tobacco and direct it toone or other of the outlets.

What I claim is:

1. Apparatus for urging material into a fluidised state and comprising atower divided by perforated flooring into a plurality of fluidisingchambers arranged one below the other, overflow ducting for transferringmaterial under gravity from one chamber to the chamber below it, aninlet for feeding material to the top chamber and an outlet forwithdrawal of the material from the bottom chamber, an inlet for gas inthe bottom chamber and an outlet for gas in the top chamber, and meansfor vibrating the material horizontally in the chambers, wherein theoverflow ducting is at least substantially vertical, the flooring isperforated to produce a pressure drop in the gas as it flows upwardsthrough it, and the outlet of each overflow ducting is controlled by aflap valve responsive to the diflerential pressure of opposing pressuresin the apparatus.

2. Apparatus according to claim 1, wherein each flap valve when closedis arranged to be urged open by the weight of material and the pressureof the gas in the overflow ducting against the pressure of the gas inthe chamber in which the valve is located.

3. Apparatus according to claim 2, wherein each flap valve isrectangular and controls a rectangular outlet in an overflow ducting,the valve being hinged along its top to the ducting and sealed along itssides to the ducting by means of flexible web members.

4. Apparatus according to claim 3, wherein each overflow ducting has aninclined bottom wall which slopes downwards to the outlet.

5. Apparatus according to claim 1, wherein the bottom of the outlet ofeach overflow ducting is level with the inlet of the overflow ducting inthe same chamber.

6. Apparatus according to-claim 3, wherein at least one flap valve hasits flap and web members made of nylon proofedwith nitrile rubber, therespective thicknesses of the flap and the web members being such thatthe flap is rigid whilst the web members are flexible.

References Cited UNITED STATES PATENTS 1,550,992 8/1925 Trump 34 -1o1,611,098 12/1926 Borner 34-'-'-33 2,639,973 5/1953 Fritz.

3,079,222 2/1963 Reeve.

3,161,483, .12/1964 Morris. J 3,2 66,788- 8/1966 Jukkola 34 1 FREDERICKL. MATTESON, IR., Primary Examiner

